This a mandatory requirement for any customer to receiver a refund, and we state it on the main page of every product and in our policy.
In the event that you are unable to use the product to create this required song, such as not owning an up-to-date version of Serum or simply not owning the Serum VST at all, we will reimburse you 100% in store credit, so you can exchange your purchase for something else. We make this as clear as possible.
You can see this policy on any of our product pages:
Source: Seen on all RPS products
Source: Seen on all RPS products on app.rocketpoweredsound.com domain
Source: Footer of all RPS product landing pages